This application claims priority from Korean Patent Application No. 2002-76995, filed Dec. 5, 2002, the contents of which are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a head-mounted display (HMD) designed to view video images when mounted on a user's head and, more particularly, to a head-mounted display using retinal direct projection and having a small size and high resolution.
2. Description of the Related Art
In general, head-mounted displays (HMDs) appear in the form of eyeglasses or helmets. AN HMD is a personal see-through device designed to display video images to a user. The HMD is considered a magnifier-type HMD, an optical relay lens-type HMD, or a retinal direct projection-type HMD depending on the optical system configuration.
While a magnifier-type HMD can produce a virtual image with a large field of view through a very small magnifier lens, it increases eye fatigue. AN HMD using a relay lens reduces eye fatigue because a viewer can observe an image displayed on the screen from a distant position, but its size is too large to be conveniently contained in a helmet. A retinal direct projection-type HMD that has an image displayed on the screen directly projected onto the retina not only reduces eye fatigue but also makes the size of a display smaller than when the relay lens is used.
FIG. 1 shows a conventional HMD using retinal direct projection technology disclosed in Japanese Patent Laid-Open Publication No. hei 3-214872 (Sep. 20, 1991).
Referring to FIG. 1, the conventional HMD includes a point light source 1 consisting of a tungsten lamp, a condensing lens 2 for focusing light emitted from the point light source 1, a plurality of reflectors 3 and 4 for converting the path of incident light, eyepieces 5, 7, and 8 consisting of three element lenses, and an image plate 6 positioned between the eyepieces 5 and 7 for producing an image by selectively transmitting the incident light. This conventional HMD device focuses the image irradiated from the point light source and produced by passing through the transmissive image plate 6 at an eyeball 9 focal point.
However, as described above, the conventional HMD cannot reduce its size because it requires a plurality of optical components such as condensing lens 2, reflectors 3 and 4, and eyepiece 5 between the point light source 1 and image plate 6. Furthermore, it cannot provide a sufficiently high resolution since an incandescent lamp is used as the point light source 1.